1. Field of the Invention
This invention relates to a hydrostatic axial piston machine having a swash plate construction. Specifically, the present invention relates to a construction in which the swash plate position can be set by at least one positioning piston pressurized with control pressure, and where a control valve is in a line leading to the positioning piston.
2. Background Information
Axial piston machines are used primarily as hydraulic pumps in hydraulic systems. During operation of these machines, it is advantageous if the displacement volume adapts to different operating conditions by changing the diagonal position of the swash plate. For this purpose, known devices normally use mechanical or hydraulic control devices which are mechanically, hydraulically or electrically actuated.
Known hydraulic control devices have at least one positioning piston engaged with the swash plate to determine the swash plate position. This will determine the displacement volume. A control valve is located in a line leading to the positioning piston to generate a control pressure operating the piston.
Electrically actuated control devices have been used to improve the control and regulation of the displacement volume adjustment. Known systems have provided a proportional valve actuated by a proportional magnet.
The proportional magnet converts an electrical control signal into a magnetic force to actuate a pressure reducing valve which moves against a spring force. The pressure reducing valve is connected to a pressure source and generates a pilot pressure as a function of the actuation. The pilot pressure displaces a spring-activated pilot piston. The travel is transmitted by an intermediate mechanical element to a control valve located on the swash plate. The pilot piston actuates the control valve mechanically. The control valve generates a control pressure from a supply pressure. The positioning piston of the hydraulic adjustment device is pressurized with the control pressure. The swash plate position is thereby adjusted. A mechanical linkage transmits the travel back to the control valve to close the valve when the swash plate reaches the desired position.
To generate the pivoting angle of the swash plate by the electrical control signal, the known systems require five conversions in the signal transmission path. Each of these conversions is subject to varying tolerances and requires physical components. Friction occurs in some of the components which is reflected in the form of hysteresis. With the control valve located directly on the swash plate, the lines leading to the positioning piston are more complex and more expensive to construct.
The object of this invention is to make an electric-hydraulic control for the swash plate which has a simple construction.